The ability of children with "Attention Deficit Disorder" to learn will be studied in relation to their ability to sustain attention. We have found that certain task-related variables affect the learning rate of unmedicated but not of medicated ADD children. They are variables which are known to control sustained attention ("vigilance") in normals. We shall systematically manipulate stimulus salience, presentation rate, pacing (external or self), reinforcement, and ambient sound level in a series of double blind drug/placebo paired associate learning studies, using four levels of drug involving 112 ADD children and 112 matched normal controls in seven studies over two years. We predict that such change in these variables as would enhance sustained attention over long periods in normals, will enhance ADD children's learning rate even over short periods of time. If stimulants enhance learning by fortifying attention, then at effective dose levels the learning rate should be free of control by these task related variables (as it also should be in normal children). The laboratory phase is followed by a double-blind field trial to determine whether dose levels conducive to optimal learning in the laboratories predict the dose level that permits optimal conduct in classroom and home. We expect the study to: help clarify the attention deficit by establishing the "vigilance decrement" in normal functioning as a model for this psychopathology; help clarify how stimulants enhance learning; contribute an objective criterion to ADD diagnosis based on the presence of a specific effect of task-related variables on learning rate; lay the foundation for an objective procedure to determine optimal treatment schedules for ADD children; suggest how tasks might be modified so as to elicit optimal performance from ADD children in the drug-free state.